New sensitive population screening procedures, such as isoelectric focusing, enzyme activity assays and the use of multiple electrophoretic conditions have uncovered considerable hidden variation at many structural loci. It has been suggested, however, that a significant portion of the newly identified variation is due to alleles at modifier genes which cause the post-translational modification of the structural gene product. Some investigators have questioned whether genetic variability assigned to structural loci in Drosophila has been greatly overestimated because of a failure to recognize the existence of such polymorphic modifier genes. Data from human populations has been reviewed for evidence of such genetically mediated posttranslational modification (GMPTM). Tnree genetic systems (glucose-6-phosphate dehydrogenase, alpha-1-antitrypsin and hemoglobin) are reviewed in detail. Each system is subject to non-genetic post-translational modification, but none of the data currently available indicates any role of GMPTM. Other data, including studies on null alleles, activity variants, population surveys and somatic cell hybrids is also reviewed. Again, no convincing evidence has been uncovered for the presence of GMPTM. It is concluded that the current estimates of polymorphism for enzymes and structural proteins in human populations have not been inflated due to the presence of polymorphism for modifier loci.
Type conversions among the three types, P, Q and M, of the P-M hybrid dysgenesis in Drosophila melanogaster were examined. Among 54 isofemale lines established from two natural populations, about 30% of the lines have shown type conversions during laboratory culture for two years. These were M→Q, Q→M, P→Q and P→M in order of frequency. In hybrid lines (HMP) started from M×P crosses, flies receiving a P type chromosome rapidly changed their cytotype away from the M toward the P or the Q type. However, in flies consisted of only M strain-derived chromosomes, cytotype conversions were comparatively slow. Similarly, P factor activities of hybrid lines increased with generation number in flies having a P type chromosome in the genome but not in flies without it. M strain-derived chromosomes were isolated to make the HMP[e] series after several generations of exposure to the P type chromosome. In these series, P type lines appeared when the P type chromosome was removed in early generations of the HMP lines. P factors did not increase, however, with the same procedures in the later generations of the HMP lines. Circumstances related to type conversions in the P-M system were discussed: (1) P and Q factors and the M states must coexist in a genome and even in one chromosome. (2) P and Q factors or cytotype determinants transpose on a certain cytotype background. (3) How do the interactions between P or Q factors and cytotypes lead to expression of dysgenic traits?
Ranunculus silerifolius var. silerifolius and var, glaber were cyto-logically examined. The karyotypes observed in var, silerifolius were classified into four different types, Matsuyama, Mugi, Otaru and Karatsu, as found in var. glaber. The F1 plants between var. silerifolius and var, glaber, both of which have the same karyotype, showed the silerifolius-type in external morphology and their meioses were normal. The features of F2′s were variable as seen in the field. Hence, it may be concluded that the external morphological variation occurred independently of the chromosomal variation, which played an prominent role in the intraspecific differentiation of R. silerifolius.
Cytogenetical study on the colchicine-induced autotetraploid of Oryzaglaberrima was carried out. As compared with the diploid, the autotetraploid increased in stomata length, length of penultimate leaf blade, pollen diameter and seed size; decreased in plant height, first internode length, number of panicles, number of spikelets per panicle, pollen stainability and seed fertility. The differences between them were conspicuous in number of panicles, number of spikelets per panicle, seed fertility and seed size. The autotetraploid had multipored pollen grains and awned seeds, which was different qualitatively from the diploid. In pollen mother cells of the autotetraploid, 2 to 12 IV were observed at the stage of diakinesis to metaphase I, and 8IV+8 II most frequently. The mean meiotic chromosome configuration was 7.63IV+0.08 III+8.51 II+0.23 I. The meiotic chromosome configurations observed in the present study could be explained by a hypothesis postulated by Jackson and Casey (1980, 1982) with random pairing among four homologous chromosome arms and a maximum two chiasmata per bivalent.
In vivo and in vitro recombination techniques were used to construct a new cloning vector, pHY300PLK (4.7 kb) from the shuttle vector pHY460 (7kb). The newly derived shuttle vector can replicate and express the tetracycline resistance gene (TcR) in both Escherichia coli and Bacillus subtilis. pHY300PLK contains the TcR gene, the ampicillin resistance gene (ApR), two replication origins for E. coli and B. subtilis and a polylinker derived from πAN7. The unique cloning sites are BalI, BamHI, BanI, BglI, BglII, BstEII, EcoRI, EcoRV, HindIII, HpaI, SalI, SmaI, PvuI and XbaI, pHY300 PLK is characterized as a copy-number mutant in E. coli. (Key words: shuttle vector; B, subtilis; tetracycline; ampicillin; copy-number mutant; incompatibility)
R-loop molecules formed between a Drosophila transposon, copia and 5kb RNA from Drosophila virus-like particles were examined under an electron microscope. It was found that 5kb RNA of virus-like particles is a genome- sized unspliced transcript of copia.
Using restriction endonuclease analysis, chloroplast DNA (ctDNA) of normal or male sterile cytoplasms in Brassica napus were compared. There were some differences in restriction patterns of ctDNA from two types of cytoplasms digested with several restriction endonucleases. Based on the fragment pattern of Eco RI digested ctDNA, there were two types of ctDNAs in B, napus and one type of ctDNA was coincident with male sterile cytoplasm, whereas another type of ctDNA was observed only in the normal cytoplasm.
The loci for ENO1, PGD, and PGM1 were regionally assigned to Chinese hamster chromosome 2 using mouse × Chinese hamster somatic cell hybrid clones containing rearranged hamster chromosomes derived from T(2; 3) 1Idr and T(2; 10)3Idr translocation stocks of the Chinese hamster. Segregation analysis of the rearranged hamster chromosomes and expression of marker enzymes indicated that these genes are located on the region 2q24→2qter. Combining the present results with those in the literature, we confirmed the previous assignment of ENO1 and PGD loci to 2q33→2qter, and narrowed the localization of PGM1 from 2q23→2q33 to 2q24→2q33.
Using each one of the four open reading frames in the P transposable element of Drosophila melanogaster, computer search of homology was carried out against the protein sequence data base of NBRF version 4. A deduced polypeptide of about 210 residues in ORF1 of the P element appears to have a significant homology with the resolvases of bacterial transposable elements Tn3 and γδ. The polypeptide seems to possess a region consisting of 22 amino acid residues having homology with DNA-binding fold of the resolvases of the bacterial transposons Tn3 and γδ, which are known to have a repressor function of the transposable elements. There are a nine base pair region in ORF3 and also in the 31 base pair inverted terminal repeat of the P element having homology with a site in the promoter region of the Tn3 and also of γδ at which the resolvases bind and suppress transcription of transposases. Based on these findings, it was suggested that the ORF1 might code a resolvase protein which mediates site-specific recombination and also suppresses the transposition of the P by binding at a specific site in the ORF3 or in the terminal repeat. It was also suggested that the whole P might code a transposase.